And they have been strengthened by senior club officials' refusal to comment on the speculation.

Ferguson took over at Old Trafford in 1986 after a successful spell at Scottish club Aberdeen, who he took to European Cup Winners Cup glory in 1981.

Since stepping into the United hotseat Ferguson has delivered unprecedented success for the club, including 13 Premier League titles and two European Cups.

Following the club's partial floating on the New York Stock Exchange last August United have to adhere to strict rules governing the release of significant information relating to the running of the club.

Ferguson's future as manager would fall within those rules, which may explain the lack of comment by the club.

Meanwhile bookmakers in the UK have seen a surge in bets on Everton manager David Moyes succeeding Ferguson at Old Trafford, forcing the odds to be slashed.

Jose Mourinho, who last week seemed to indicate he was heading back to England to coach, is another who will be in contention for the role should Ferguson quit.

The 71-year-old Scot is due to have hip surgery in August, just two weeks before the start of the new football season.